1. Field of the Invention
The present invention is directed to a method for the operation of a digital imaging system of an X-ray diagnostic apparatus, of the type having an X-ray unit for the production of X-rays, an X-ray image converter/television chain for the acquisition of the X-ray images, the chain including a digital image converter having image points arranged in matrix form in rows and columns and a monitor for the reproduction of the X-ray images processed by the digital imaging system.
2. Description of the Prior Art
In medical technology, digital imaging systems, in which digital image converters replace the previously employed analog image converters, are becoming increasingly important. Image converters of this sort that are used, e.g. amorphous silicon detectors, in general still cannot be produced without flaws. Alongside defective pixels or image points, failures of clusters, lines and columns also occur. Thus, for example, column failures are caused by interruptions in the address lines.
In order to limit the rejection of detectors, the defective image points can be corrected. For a successful correction, it is necessary to know which pixels are defective and which are good.
Previously, several dark images (images without radiation) and several sets of bright images, i.e. objectless images with radiation, were obtained with different intensities, and a dark current-corrected image was produced through an arithmetic combination. It was then attempted to find the defective pixels from these images. This could, for example, take place using histograms and predetermined threshold values in the histogram curve, or using a sum of histograms for different regions of the image, or by checking of all the image points of the image with certain range limits.
All these methods, or similar ones, however lead to problems if, for example, the electronic characteristics of the system change with a new detector or other modes of operation of the detector, since they primarily depend on a plurality of parameters that must first be determined for a particular detector unit.
In a copending application, a method for defect recognition in an amorphous silicon panel is described, in which, for the recognition of defective image points, a recursive lowpass filtering according to the principle of fuzzy masking, with separation of the defects according to rows and columns, is multiply applied to two images, of which a first image is produced with X-ray radiation without an object, and a second image is produced without X-ray radiation.